How Trees are Multiplied 



different subject. Its variations come through the seeds. Here 

 the pollen, scattered in various ways when plants blossom, falls 

 on the pistils of flowers somewhat indiscriminately. Especially 

 is this true of wind-fertilised flowers which produce pollen in 

 abundance and of a dry, powdery sort. The pollen lies inert on 

 the stigmas of alien species. It fertilises those of its own kind. 

 There are intermediate varietal relationships and very closely 

 related species in certain families. In these cases natural crosses 

 occur, flowers being fertilised by pollen of another species. Seeds 

 thus set produce hybrid plants, new kinds having characters of 

 their two parents. Thus the species of willows are hopelessly 

 intermixed. Natural crosses between oaks are frequently dis- 

 cernible in the woods. The white oak crosses with several 

 species in its own (annual) group. The biennial or black oaks 

 also intercross among themselves. But black and white oaks 

 do not cross. 



Artificial crosses are frequently made by plant breeders 

 for scientific and economic reasons. Some of the best horticultural 

 varieties of fruits and flowers are artificial hybrids. Among these 

 are the Kieffer pear, the wild goose plum, and various roses, 

 grapes, begonias, cannas and pelargoniums. Hybrids are propa- 

 gated by division. 



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